The present invention relates to techniques for writing data in disk drive systems, and more particularly, to write drivers that provide write current to write elements in disk drive systems.
Magnetic data storage devices, and in particular hard disk drive storage devices, have become an essential component in modern computer systems. An example of a well-known hard disk drive storage device 100 is shown in FIG. 1. Hard disk drive 100 includes an enclosure 101 that contains one or more magnetic media platters or disks 102, read elements 104, write elements 105, an actuator arm suspension 106, a transmission line interconnect 108, a read/write integrated circuit (IC) 110, a flexible interconnect cable 112, and a disk enclosure connector 114.
Magnetic media disks 102 store information on their surfaces. Read elements 104 and write elements 105 are mounted on actuator arm suspension 106 and are located in proximity to the surfaces of disks 102. Actuator arm suspension 106 moves the read/write elements into proximity to a selected portion of disks 102 that contains the information to be read, or that has open area where new information is to be recorded. Write elements 105 write information in response to input electrical signals, and read elements 104 read recorded information and output electrical signals representing the information.
The electrical signals are communicated between the read/write elements and read/write integrated circuit 110 over transmission line interconnect 108. Read/write integrated circuit 110 conditions the electrical signals so that they can drive write element 105 during writing and amplifies the electrical signal from read element 104 during reading. Signals are communicated between read/write integrated circuit 110 and disk enclosure connector 114 over flexible cable 112. Disk enclosure connector 114 conducts signals with circuitry external to disk enclosure 101.
A profile view of the structure of hard disk drive 100 is shown in FIG. 2 with two disks 102A and 102B. Disk drive 100 has four read elements 104A-D and four write elements 105A-D. After read/write integrated circuit 110 selects one of the read or write elements, data is read from, or written to, the selected element.
Read/write IC 110 typically includes a write driver that drives current to one of the write elements. Typical write driver circuit designs consume a considerable amount of power. These high-power designs cause an undesirably large amount of heat dissipation through the actuator.
In a typical hard disk drive storage system, the read/write integrated circuit 110 is located relatively far away (approximately 5 cm) from the read and write elements. Because of the length of the transmission line interconnect between circuit 110 and the read/write elements, it is difficult to obtain the desired performance when writing information to the disk. The time it takes for the write current from the write driver to reverse is typically in the sub-nanosecond range at higher data rates, which creates design challenges for the output impedance of a typical write driver circuit design.
Typically, the write driver's output impedance-value configuration is set to be equivalent or greater than the characteristic impedance of the transmission line interconnect. With this value configuration, the write signals are well behaved or can have some overshoot, for when the output impedance is greater than the transmission line interconnect impedance. If the write element's impedance is mismatched with the characteristic impedance of the transmission line interconnect, signal reflections from the write element can occur. The reflected signal is then terminated at the output port of the write driver's output. The reflected signal can interfere with the transmitted signal, causing distortion and degrading signal integrity.
Therefore, it would be desirable to provide a write driver circuit that consumes less power, obtains a higher performance, and minimizes signal reflection on the transmission line interconnect.